JP-A-2002-361931 discloses an image forming apparatus exposing a photosensitive drum by the use of an LED head, in which a spacer maintaining a gap in an optical axis direction between the LED head and the photosensitive drum is disposed between the LED head and the photosensitive drum. In the image forming apparatus, the spacer is formed integral with the LED head.
Since the spacer is formed integral with the LED head, the spacer coming in slide-contact with the rotating photosensitive drum may be attracted in a rotation direction of the photosensitive drum due to the friction with the photosensitive drum and thus the LED head may move in the rotation direction. Accordingly, it can be considered that a positioning member is disposed downstream of the LED head in the rotation direction to regulate the position of the LED head in the rotation direction. However, when the spacer is attracted in the rotation direction of the photosensitive drum, the LED head may be inclined about the positioning member. In this way, when the LED head is inclined, the gap in the optical axis direction between the photosensitive drum and the LED head varies. When the photosensitive drum rotates and comes in slide-contact with the spacer and thus the spacer is abraded, the gap in the optical axis direction between the photosensitive drum and the LED head varies. As a result, since a focal position of light emitted from the LED head is changed, the image quality is deteriorated.